• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.26 no.11
• /
• pp.2457-2465
• /
• 2002

Numerical modeling of a nondestructive testing system plays an important role in many aspects of quantitative nondestructive evaluation (QNDE). The ultimate goal of a model is to predict test results for a specific flaw in a material. Thus, in ultrasonic testing, a system model should include the transducer, its radiation pattern, the beam reflection and propagation, and scattering from defects. In this paper attention is focused on the scattering model and the scattered fields by defects are observed by an elastodynamic boundary element method. Flaw types addressed are void-like and crack-like flaws. When transverse ultrasonic waves are obliquely incident on the flaw, the angular distribution of far-field scattered displacements are calculated and presented in the form of A-scan mode. The component signals obtained from each scattering problem are identified and their differences are addressed. The numerical results are also compared with those obtained by high frequency approximate solutions.

• Journal of Industrial Technology
• /
• v.19
• /
• pp.127-133
• /
• 1999

This paper is a research about system identification which optimizes uncertain geothechnical properties from the data measured during geotechnical design and construction. Various numerical optimization algorithms of Simplex method, Powell method, Rosenbrock method and Levenberg-Marquardt method were applied to the excavation problem to determine which method showed the best results with respect to robustness of success in finding an optimal solution to within a certain accuracy and number of function evaluations. From the results of numerical analysis, all of four algorithms are converged to exact solution after satisfying the allowed criteria, and Levenberg-Marquardt's algorithms was identified to be the most efficient method in number of function evaluations. System identification was applied to geotechnical engineering problems, possibly being occurred in field, to verify its applicability : estimation of settlement due to self-weight consolidation in dredged and filled soil. For self-weight consolidational settlement of a dredged soil, a program of evaluating the constitutive relationship of effective stress-void ratio-permeability was developed by using the technique of system identification. Thus, consolidational characteristics of a dredged soil, having a very high initial void ratio, can be evaluated.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2007.04a
• /
• pp.487-492
• /
• 2007

The enhancement of the service life of damaged or cracked structures is a major issue for researchers and engineers. The hierarchical void element with the integrals of Legend polynomials is used to characterize the fracture behavior of unpatched crack as well as repaired crack with bonded composite patches by computing the stress intensity factors and stress contours at the crack tip. The numerical approach is based on the v-version degenerate shell element including the theory of anisotropic laminated composites. Since the equivalent single layer approach is adopted in this study, the proposed element is necessary to represent a discontinuous crack part as a continuum body with zero stiffness of materials. Thus the aspect ratio of this element to represent the crack should be extremely slender. The sensitivity of numerical solution with respect to energy release rate, displacement and stress has been tested to show the robustness of hierarchical void element as the aspect ratio is increased up to 2000. The stiffness derivative method and displacement extrapolation method have been applied to calculate the stress intensity factors of Mode I problem.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2009.09a
• /
• pp.1170-1180
• /
• 2009

Recently this country has carried out the coast reclamation centering on the west and south coast for effective practical use of a country, considering purchase of materials and environmental problem, most reclaiming work is processing to spoil reclamation which is easy to secure the amount of materials. In case of weak ground that is formed by spoil reclamation like this, initial moisture content is high, as slurry state that is rarely revealed ground strength, compressibility and water permeability have been shown nonlinear change by compaction progress. Analysis of weak ground is unreasonable because the existing Terzaghi compaction theory analyzes compaction fixed number to regular invariable number for prediction of compaction state. This study computes the relation with void ratio-effective pressure and void ratio-finite transformation which is the most basic matter to predict finite strain compaction state of the south coast spoil, and analyze the basic feature to predict compaction feature of the south coast spoil reclaimed ground.

• Korean Institute of Interior Design Journal
• /
• no.20
• /
• pp.84-90
• /
• 1999

This study is on relations between minimalism, which is one of important theme in the contemporary design, and East-oriented speculatiov. Minimalism, one inclination of neo-modernism is characterized by Essentialism. That is connected with East-oriented thinking, especially Taoism. The paradigm of contradiction and paradox replaces the paradigm of rationality and the law of cause and effect. Minimal tendency is appeared at Modernism in 60's and Neo-modernism in 90's. The differences are originated with their manner on simplicity. Minimal tendency in Modernism is characterized by 'less is more' and that in Meo-modernism is by 'more with less'. The minimizing strategy is not considered as means as in modern age but as purpose in neo-modern age. This paper explains minimal architectural space as spatial problem and recognitions on that, not as the figurative problem. Conclusively the relationships between minimalism and eastern ideas are represented through the boundary and extensity of space, void and solid, de-formalization and Essentialism.

• Geomechanics and Engineering
• /
• v.25 no.4
• /
• pp.283-294
• /
• 2021

This paper presents a rigorous solution for spherical cavity expansion in unsaturated soils under constant suction condition. The hydraulic behavior that describes the saturation-suction relationship is modeled by a void ratio-dependent soil-water characteristic curve, which allows the hydraulic behavior to fully couple with the mechanical behavior that is described by an extended critical state soil model for unsaturated soil through the specific volume. Considering the boundary condition and introducing an auxiliary coordinate, the problem is formulated to a system of first-order differential equations with three principal stress components and suction as basic unknowns, which is solved as an initial value problem. Parameter analyses are conducted to investigate the effects of suction and the overconsolidation ratio on the overall expansion responses, including the pressure-expansion response, the distribution of the stress components around the cavity, and the stress path of the soil during cavity expansion. The results reveal that the expansion pressures and the distribution of the stress components in unsaturated soils are generally higher than those in saturated soils due to the existence of suction.

• Journal of Korean Society of Steel Construction
• /
• v.23 no.6
• /
• pp.705-713
• /
• 2011

This study was conducted to assess the vibration capacity and the fire resistance capacity of a deck plate slab using an omega steel plate as the void deck plate. First, to evaluate the vibration capacity of the deck plate slab after the insertion of the omega steel plate, three 150mm specimens and three 200mm specimens were made using the slab depth as the main variable. Each specimen consisted of an existing deck plate and two specimens, using the topping depth as the variable according to the slab depth. Second, two real-size specimens were made to evaluate the fire resistance capacity. The results of the test showed that the steel-wire-integrated deck plate slab that was inserted in the omega steel plate did not have a vibration problem due to the void deck plate, because the natural frequency was 12.66-14.09 Hz in the vibration test, and each specimen satisfied the appraisal standards for the load capacity, heat block quality, and chloride inhibition for two hours in the fire resistance test. Consequently, the steel-wire-integrated deck plate slab that was inserted in the omega steel plate can be reduced using the concrete volume and can have higher vibration and fire resistance capacities, similar to the existing deck plate.

• The Journal of Korean Philosophical History
• /
• no.27
• /
• pp.7-37
• /
• 2009

This paper handled the problem of 'the mind' suggested by Bojo-Jinul. On the whole, I explained three fields, Jinul's way to approach 'the mind', the theory of the nature and the theory of practice and enlightenment. This paper is based on the established research papers. However the part that I explained the 'no-mind' in the theory of the nature is different from the established researchers. It is the emphasized part to interefere with Kanhwa Meditation. In this part, I explained Bojo's way to approach 'the mind' in the viewpoint of Sujeungnon(the theory of practice and enlightenment). And I clarified that his thought had been showed in his work and his system of thought is composed of Donojeomsuron(the theory of sudden enlightenment and gradual cultivation) and Kanhwa-Seon(Kanhwa-meditation). It is the theory of the nature that we handles 'the problem' philosophically. So I studied the examples of the nature and then I researched 'Kongjeokyeongjisim(the mind of the light of the divine wisdom in the void)', the foundation of 'Donojeomsu(the sudden enlightenment and gradual cultivation)' and 'Musim (no-mind)', the foundation of Kanhwaron. Finally, I inquired into 'Donojeomsuron(the theory of sudden enlightenment and gradual cultivation)' and 'Kanhwaron(Kanhwa-Meditation)' as 'Sujeungron(the theory of practice and enlightenment)'.

• Journal of Advanced Marine Engineering and Technology
• /
• v.26 no.4
• /
• pp.464-471
• /
• 2002

Porosity formation in partial penetration welds by high power lasers is a serious problem in industry. There are two main causes that induce porosity formation. One form of porosity is due to gases (e.g. hydrogen, oxygen) dissolving into the weld pool because of the high temperature and then the rapid solidification traps gases as a bubble in the weld metal. The second problem is voids formed by the keyhole collapsing due to unstable keyhole fluid dynamics. The voids that form at the bottom of the keyhole are relatively large and irregular in shape compared to the gas bubbles; this void formation is the primary concern in this paper. The reduction of voids formed by keyhole collapse is achieved by improving the stability of keyhole. Two methods to improve keyhole stability are discussed in this paper: pulse modulation and beam incident angle. Pulse modulation of the laser beam was performed between 100 Hz and 500 Hz to find out the optimum frequency for the keyhole dynamics. The incident beam angle changed the impact angle of the laser beam to the work surface in a range of 0 to 25 degrees. Glycerin in a semi-solidified state is used as a medium for performing the welding because its transparency allows of visualization of the keyhole.

• ETRI Journal
• /
• v.44 no.5
• /
• pp.715-732
• /
• 2022

Despite the successful launch of Advanced Television Systems Committee (ATSC) 3.0 broadcasting worldwide, broadcasters are facing obstacles in constructing void-less large-scale single-frequency networks (SFNs). The bottleneck is the absence of decent on-channel repeater (OCR) solutions necessary for SFNs. In the real world, OCRs suffer from the maleficent feedback interference (FI) problem, which overwhelms the desired input signal. Moreover, the undesired multipaths between studio-linked transmitters and the OCR deteriorate the forward signals' quality as well. These problems crucially restrict the feasibility of conventional OCR systems, arousing the strong need for cost-worthy advanced OCR solutions. This paper presents an ATSC 3.0-specific solution of advanced OCR that solves the FI problem and refines the input signal. To this end, the FI canceler and channel equalizer functionalities are carefully implemented into the OCR system. The presented OCR system is designed to be fully compliant with the ATSC 3.0 specifications and performs a fast and efficient signal processing by exploiting the specific frame structure. The real product of ATSC 3.0 OCR is fabricated as well, and its feasibility is verified via field and laboratory experiments. The implemented solution is installed at a commercial on-air site and shown to provide substantial coverage gain in practice.